One conventional form of sewing machine requires, for effective operation, two separate supplies of thread, one leading directly into the sewing needle and the other supplied from a small bobbin located on the opposite side of the article being sewed. A so called lock stitch is formed by penetrating the article from one side with a length of thread, drawing enough thread through to form a loop, passing the loop around the small bobbin to engage the bobbin thread, and then withdrawing the loop to form the lock stitch. Because the needle thread must be formed into a loop and passed around the bobbin, the bobbin must be of small diameter and thus necessarily contains a relatively limited supply of thread. Accordingly, in a high speed industrial sewing operation utilizing lock stitch techniques, it is necessary frequently to change bobbins as the bobbin in use becomes depleted of its thread supply. The used bobbins are, of course, rewound with new supplies of thread for subsequent use. The bobbin exchange and rewinding is a time consuming, repetitive operation which can significantly impair the efficiency of high speed sewing equipment. It is thus an objective of the invention to provide a mechanism which can be incorporated directly in a high speed sewing machine to effect automatic, high speed rewinding and exchange of bobbins.
One of the features of the invention resides in the provision of a noel high speed transfer mechanism, comprising a pair of transfer arms rotatable about an axis and also movable along the axis. The transfer arms are provided and combined with novel mechanisms which facilitate separation of the bobbin from the bobbin case, in the rewind position, while enabling the bobbin and bobbin case to be retained together in the sewing position. Among other things, this aspect of the mechanism includes a controllably actuated magnetic holder for separating the bobbin from its bobbin case, the case being retained by the transfer arm. In this connection, the transfer arm itself includes an advantageous form of mechanism which simultaneously grips the bobbin case and releases the mechanical locking means by which the bobbin normally is secured in the sewing machine.
During execution of a bobbin reloading operation, one of the steps involves reassembling the freshly wound bobbin into its bobbin case and guiding the thread underneath the bobbin case tension spring. The mechanism of the invention includes novel and relatively simplified facilities for accomplishing this objective on a reliable, automatic basis.
In order to avoid the need for manual intervention in the bobbin exchange process, it is necessary to maintain control at all times over the thread supply, not only to enable the thread to be properly engaged with the bobbin case tension spring, as just described, but also to enable the thread to be brought into the proper position relative to the sewing mechanism, where the bobbin is inserted in the sewing position. Thus, as another objective of the invention, provision is made for maintaining the thread end, extending from the bobbin case tension spring, under complete control throughout the bobbin exchange process and placing it in a predetermined position relative to the sewing mechanism, upon completion of the exchange. To advantage, this is accomplished by effecting the bobbin transfer manipulations while the filled bobbin is still connected to the primary thread supply. As the bobbin and bobbin case are manipulated from the winding position to the sewing position, the attached thread moves with the freshly wound bobbin and is picked up by strategically placed guide elements. When the newly wound bobbin is finally inserted in the sewing position, the trailing thread is positioned in a predetermined control path where it can be clamped, cut, positioned for sewing and also reengaged with the empty bobbin for a subsequent rewinding cycle.
In accordance with another feature of the invention, a novel and highly simplified arrangement is provided for enabling the rewinding of a new bobbin to commence without manual intervention. To this end, the invention includes a slightly modified form of bobbin, provided with a thread pick up slot, in conjunction with a movable thread guide. The latter engages a section of thread in the span leading from the primary supply, around the control path and up to the freshly wound bobbin in the sewing machine. When the rewinding operation is ready to commence, the thread guide is actuated in a manner to press the control thread against the end face of the bobbin, passing it through the pick up slot and causing the thread to be engaged by the rotating bobbin for rewinding.
In accordance with another feature of the invention, improved overall sewing efficiency is achieved by effecting a bobbin reload before the bobbin in use is fully exhausted of its thread supply. This prevents from running out of bobbin thread in the middle of a sewing operation and possibly resulting in a defective product. While this is of course a widely used technique, it is an objective of the invention to enable the technique to be utilized in a two bobbin, automatic rewind system forming an effectively integral part of the sewing machine. To this end, the system of the invention includes provisions for initially reversely rotating the bobbin when it is in the rewind position, in conjunction with a vacuum nozzle for extracting unused thread. Thus, in a sequence of operations with the mechanism of the invention, the used bobbin, after separation from its bobbin case and mounting in the rewind position, is reversely rotated while the excess thread is extracted by vacuum. The bobbin is then rotated in a winding direction and the rewind thread guide is actuated to cause the control thread to be engaged with the bobbin pick up slot.
A further feature of the invention is the provision of automatically operative means for separating and disposing of the short span of control thread which extends from the rewinding position to the sewing position after completion of a bobbin exchange manipulation.
For a better understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description and to the accompanying drawings.